The diversity of modern technical applications creates a need for efficient electronic components and integrated circuits for use therein. Capacitors are a fundamental component used for filtering, coupling, bypassing and other aspects of such modern applications which may include wireless communications, alarm systems, radar systems, circuit switching, matching networks, and many other applications. A dramatic increase in the speed and packing density of integrated circuits requires advancements in coupling capacitor technology in particular. When high-capacitance coupling capacitors are subjected to the high frequencies of many present applications, performance characteristics become increasingly more important. Since capacitors are fundamental to such a wide variety of applications, their precision and efficiency is imperative. Many specific aspects of capacitor design have thus been a focus for improving the performance characteristics of capacitors.
The incredible variety of capacitor environments implies that capacitors are often subjected to a number of different operating frequencies. Many wireless communications systems, including satellite, GPS, and cellular applications, as well as high speed processor applications require capacitor technology that can accommodate high frequencies of operation. As such, wideband capacitors have been previously provided in several forms to accommodate incorporation into many different types of electronic equipment. In several of these previously known configurations, emphasis has been placed on providing plural capacitive elements within a single structure. Such plural elements have taken many forms including physically separate devices electrically coupled together and plural element device design to produce secondary components that function as additional capacitive elements within the single device.
U.S. Pat. No. 6,816,356 to Devoe et al. is one such device. Devoe et al. provide an integrated capacitor array including a plurality of capacitors connected in series and/or parallel circuits in a substantially monolithic dielectric body. The device includes both a multi-layer lower frequency, higher value capacitor and a higher frequency, lower value capacitor.
U.S. Pat. No. 7,248,458 to Mruz discloses another example of wideband capacitor construction providing both a low frequency portion and a high frequency portion. As illustrated herein in FIGS. 1A-1J, Mruz's wideband capacitor is constructed using a fairly complex and expensive production technique.
FIGS. 1A-1J depict construction of a wideband device in accordance with Mruz's teachings. As illustrated in FIG. 1A, device 100, is a standard multilayer capacitor (MLC) without termination. Capacitor 100 consists of alternating electrodes 102, 104 in a ceramic structure 110 that provides the dielectric separating electrodes 102, 104.
FIG. 1B illustrates a cross-section of capacitor 100 taken along line A-A of FIG. 1A. After formation of capacitor 100, an overall coating of conductive metal 120, usually electroless nickel followed by an electroless gold flash, is applied on all six sides of capacitor 100. Following coating with conductive metal 120, cut 130 through conductive metal 120 is provided by suitable means to isolate the two polarities of capacitor 100, represented in FIG. 1C as terminal portions 132, 134. FIG. 1D illustrates a cross-section of capacitor 100 similar to that illustrated in FIG. 1B showing the cut 130 into conductive metal coating 120 producing separated terminal portions 132, 134.
Next, as illustrated in FIG. 1E, an insulative coating 140 is applied over the now separated portions 132, 134 of conductive metal coating 120. Insulating layer 140 may generally correspond to an epoxy coating. It will be appreciated that, as illustrated in the capacitor cross-section of FIG. 1F, the insulating coating 140 will generally fill the gap created by cut 130. After the epoxy, or other insulating material, is cured, the part is either batch plated or dipped into termination paste at each end, forming solderable terminals 152, 154 as illustrated in FIG. 1G. The completed part is now shown in longitudinal cross-section in FIG. 1H.
Due to the configuration of the completed structure, additional capacitances are formed as shown in FIG. 1I at area 164 between top electrode 102a and the circumferential plating 134, as well as at area 165 between the bottom electrode 104a and the plating 132. These additional capacitances are represented as areas 164 and 165. Similarly there is a capacitance, albeit quite small, between the end of the electrodes and the end plating, which is represented as areas 166 and 167. The major capacitance comes from the overlap area inside the MLC, which is represented as area 162.
These various capacitances are represented schematically at low frequencies in FIG. 1J. The large overlap area 162 gives rise to the schematic capacitor 162′. The second areas 164 and 165 contribute to the capacitance 164′, 165′ and the small end capacitor areas 166 and 167 give rise to capacitor 166′, 167′. Common cross hatching relates the areas to the capacitors. The resulting equivalent capacitive circuit of different value capacitors in parallel provides for a broad-band response.
While the prior art has provided various methodologies for constructing wideband capacitive components, it would, nevertheless be advantageous to provide similar or improved results at a significant reduction in production effort and cost.
While various implementations of wideband capacitors have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.